The present invention relates to a mapping system and method using Light Detection and Ranging (LIDAR) technology. More specifically, the present invention relates to software that integrates multiple modules and subsystems into a single user-friendly mapping system.
Advancements in Light Detection and Ranging (LIDAR) technology have made it possible to compile digital terrain data from an aircraft platform through laser distance measurements. When integrated with airborne global positioning system (GPS) and inertial measurement systems, LIDAR can capture extremely accurate digital terrain data without GPS land surveys.
Because LIDAR data is captured real-time in an aircraft, digital terrain generation can begin before aerial photography is processed, ground control acquired, and analytic triangulation performed. Once analytic triangulation is finished, final edits and corrections can be performed using photogrammetric methods.
LIDAR works using a scanning laser unit mounted on an aircraft. As the aircraft flies along a line, the laser unit emits a stream of light pulses in a side-to-side motion perpendicular to the aircraft""s direction of flight. The time it takes for each pulse to return to the aircraft is recorded along with the angle from nadir at which each pulse was emitted. Airborne GPS data and inertial navigation data provide are also recorded during a mission.
During post processing, the slant distance between the aircraft and the ground for each returned pulse is calculated. Each slant distance is then corrected for atmospheric conditions, and for the roll, pitch and yaw of the aircraft using the inertial navigation data. Typically, GPS data is processed separately and imported into the LIDAR solution where each corrected slant distance is transformed to a ground surface elevation.
LIDAR is extremely accurate. Lower flying altitudes provide a smaller laser spot size or footprint than higher flying altitudes, allowing for more accurate data. Operating altitudes for LIDAR projects typically range from 400 meters to 1,200 meters. Some units have extended capabilities that allow higher operating altitudes.
Horizontal accuracy is typically {fraction (1/2,000)}th of the flying height. Vertical accuracy is better than 15 centimeters when the operating altitude is 1,200 meters or below, and up to 25 centimeters when the operating altitude ranges from 1,200 meters to 2,500 meters.
A significant factor in the digital terrain model accuracy is the airborne GPS data. If flight plans are optimized for GPS, then vertical accuracies of 7 to 8 centimeters can be routinely achieved. Other rules of thumb related to accuracy include:
The slower the aircraft, the denser the spot spacing.
The denser the spot spacing, the more reliable the digital terrain model (more data yields better accuracy).
Laser spots at nadir are more accurate than spots at the outside edge of the swath, or field of view.
The narrower the swath, the faster the scan rate; thus, denser data will be produced for a given pulse repetition rate and aircraft speed.
LIDAR allows generation of digital terrain models in areas with hills, heavy vegetation, or shadows. This often eliminates the need for survey crews to return to the field to capture points that could not be compiled photogrammetrically.
Points can even be captured with LIDAR where ground access is limited such as in high-security installations. Likewise, it can be used for hydrochannel mapping, shoreline mapping, and for obstruction analysis mapping for airports. Also, LIDAR is useful for mapping areas with poles and towers and to obtain the elevations of power lines (these cannot be acquired using conventional photogrammetric methods).
LIDAR is a complicated data intensive system that requires the integration of multiple data components in order to achieve accurate results. In order to generate maps based on LIDAR, data from the LIDAR laser module itself must be collected along with GPS and inertial navigation data.
What is needed is a system that integrates many of the data intensive modules that comprise a LIDAR mapping mission as well as a system that provides flight planning and real-time flight path feedback data to the pilot of the aircraft. The flight planning and flight path feedback elements allow for more efficient, accurate, and robust LIDAR mapping missions by continuously informing pilot(s) of any detected course deviations with respect to the desired flight path.
The present invention is a rapid terrain visualization-navigation (RTV-NAV) flight management and planning system and software package intended to assist an operator of a LIDAR module in planning and conducting aerial mapping surveys. The core RTV-NAV functions include flight management, survey planning, LIDAR module control, coverage evaluation, and training.
The primary RTV-NAV software display control interface includes various instrument control frames and a large navigation map. The navigation map displays current aircraft position, a trace of aircraft movement for the past few minutes, a survey grid, and a configurable map background. The navigation map can be panned and zoomed at will by the operator. The map background comprises any combination of USGS vector maps, user-definable navigation points, and pre-rendered images including graphics interchange format (GIF) images, joint photographic experts group (JPEG) images, and bitmap (BMP) images.
Real-time GPS data is acquired by listening to Ethernet broadcasts from a position and orientation system/airborne vehicle (POS/AV) inertial navigation unit built into the LIDAR module. Remote computer control of the LIDAR module is provided through a serial link between the LIDAR module and a computer running the RTV-NAV software. The serial link allows the operator to turn the LIDAR laser on and off, reconfigure the laser scan angle or scan frequency, and eject a data tape.
Flight planning capabilities are provided through a survey planner. The survey planner subsystem allows the operator to define mission parameters such as survey area, desired resolution, altitude, and aircraft velocity. The survey planner automatically calculates the necessary LIDAR parameters and flight lines. The survey area may be defined either by entering coordinates, by drawing polygons on the navigation map, or by importing coordinates from a text file.
A course deviation indicator (CDI) is provided to the pilot(s) by use of a dual-display video card. One display, containing the primary RTV-NAV operator interface, is shown to the system operator while the other is dedicated to the CDI. This second display is then typically scan-converted to video and fed to a cockpit television or flight management system (FMS). The CDI is a real-time instrument capable of showing the pilot(s) both graphically and numerically the aircraft""s perpendicular distance from the current desired flight line. The CDI also provides course and distance-along-line information, as well as a LIDAR on/off indicator. Finally, the CDI includes a crude mini-map representation of the aircraft position with respect to the flight line for gross situational awareness.
Real-time coverage tracking is provided through a plan progress window that provides a map of the survey area including flight lines. When the aircraft passes through the planned survey area while the LIDAR is activated, the resulting laser swath traced on the ground is drawn on a plan progress display. This swath is determined from the real time GPS position and inertial orientation data provided by the POS/AV inertial navigation unit, and the LIDAR ranges. If the GPS data is good, as defined by several GPS quality indicators, the swath will be drawn in green. If the GPS data is questionable, the swath will be drawn in red. As multiple lines are flown, coverage gaps between lines can easily be seen, and additional lines may be flown to fill them. The information necessary to later reconstruct these swaths is stored.
During a flight, the system operator loads a pre-made flight plan, and uses the primary RTV-NAV control interface to select flight lines for the pilots as the flight progresses. The pilot CDI display will automatically be set to the flight line selected by the system operator. As the resulting area coverage is drawn on the plan progress display, new flight lines are chosen to either cover new flight lines or fill in gaps between previous flight lines as necessary. The RTV-NAV software control interface is used to turn off the LIDAR module while the aircraft is turning around, and to re-activate the LIDAR module when a new flight line is begun. The RTV-NAV system also maintains an automated log of all LIDAR module settings, flight lines, GPS problems, and operator.